FS 10
June 1962
AVALALL
Controlling Moss on Roofs
Prepared by I. C. MACSWAN, Extension Plant Pathologist, and
M. G. HUBER, Extension Agricultural Engineer
Oregon State University
Moss is a simple form of plant growth that thrives
in damp, shaded locations. It is likely to be found on
the north slopes of roofs and roofs shaded by overhanging trees.
Control measures include removal of overhanging
branches, scraping away as much moss as possible,
and spraying the area with chemical. Spraying is most
effective in warm weather when the moss is active1y
growing, and when rain is not likely for several days.
Zinc chloride
Spray moss with a 10% solution. Zinc chloride is
corrosive to metals and injurious to plants.
Arsenic compounds (sodium arsenite, arsenic
trioxide)
Spray surface of moss with solution of to ounce
in 10 gallons of water. Arsenic compounds are very
poisonous to humans and animals and are injurious to
plants. Arsenic solutions have fair residual effect.
Table salt
Recommended Materials
Zinc galvanized or copper flashings and ridges
A galvanized or copper ridge will be effective for
about 10 to 15 feet down from the ridge on most roofs.
Normal corrosion from bare copper wires, stretched
about every 10 feet horizontally along the butt ends
of shingles, will provide some moss control.
Pentachiorophenol
This material can be used as a water solution or
mixed 50-50 with diesel oil. Water solution: Prepare
a 5% solution according to the directions on the container label. Diesel oil mix (do not use on asphalt roofs
since the oil will dissolve the asphalt) : Mix equal parts
of pentathlorophenol and diesel oil.
Several applications of pentachiorophenol on wood,
shingle, or shake roofs will provide good moss control
for some time.
Sodium pentachiorophenate (5% solution)
To prepare 5 gallons of 5% solution, mix 2 pounds
of sodium pentachlorophenate powder in 5 gallons of
water. Sodium pentachlorophenate solutions may be
used safely on asphalt roofs.
Copper sulfate (blue stone)
Copper is effective when sprayed on moss at the
rate of to ounce per 10 gallons of water. It is corrosive to metal eave troughs, down spouts, and metal
spray equipment and they should be washed thoroughly
with water immediately after treatment. Copper sulfate
solution has a good residual effect, depending on type
of roof, amount of penetration, and amount of rainfall.
Spray surface of moss with 10% to 20% solution
or sprinkle dry table salt when moss is wet. Table salt
does not have a residual effect and is not as effective
as some of the other materials. Table salt is also corrosive to metals and injurious to plants.
Mercury compounds
Some mercury-containing fungicides are being recommended for moss control. Follow the manufacturer's
recommendations for safe and effective use. Mercurycontaining compounds are very poisonous to humans
and animals.
Other weed killer compounds
Some compounds normally used as weed killers are
also effective for moss control. Follow the manufacturer's directions and precautions for use.
Cautions
Use extreme care when applying the materials
mentioned above. Keep them from children and animals
and prevent contamination of plants. Be sure that spray
does not fall or drift onto plants and that spray solution is not carried down drainspouts to injure plants
in foundation plantings. Use of a sprinkler can for
applying solutions may reduce the drift hazard.
Remember that several of the chemicals recommended for control of moss are very corrosive to metal.
Be sure gutters and down spouts are clear, so solutions
washing off treated roofs do not stand in troughs.
Thorough flushing with fresh water may save costly
replacement of metal gutters. Equipment can be protected by adding 2 tablespoons of household ammonia
to a gallon of water for the final flushing through the
sprayer.
This is one of a series of Fad Sheets reporting Cooperative Extension work in agriculture and home economics, F. E. Price, director. Printed and distributed in furtherance of Acts of Congress of May 8 and June 30,
1914. Oregon State University, Oregon counties, and U. S. Department of Agriculture cooperating.